It started burning a quart every 2,000 miles

then every 1,200

now it's burning a quart every 500 miles right now.

Could it be valve seals? Darn well better be something minor;
Second-Stage engine by MB, here!

What other possibilities could it be? A lot of people are unfamiliar with these 3.5 engines and their different mechanical characteristics from the 3.0.

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1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)